Several fabrication features cause a reduction in the accuracy and durability of capacitive sensors. The use of different materials on the top and bottom surfaces of the capacitive gap leads to thermal mismatch between the top and bottom of the gap. Use of metal electrodes limits the ability to form a high temperature fusion bond between two wafers, which limits the ability to seal the device hermetically. Construction of a pressure port on the same surface as the wirebond pads leads to a difficult exposure problem of the wirebond pads to the harsh media being measured.
Current fabrication methods address some of these concerns, but not others. For example, many methods use electrically conductive metal vias to place electrical interconnects on the opposite side of a sensor from the active sensor elements. However, these fabrication methods have several disadvantages. For example, extra fabrication steps must be used to pattern the electrically conductive metal vias in the sensor. In addition, the use of metal gives rise to the complications described above. Accordingly, there is a need in the art to develop methods of fabricating capacitive sensors that allow hermetic sealing, reduce or eliminate thermal mismatch, and limit exposure of wirebond pads